Beautified C9

styles.css

/* colors:
 * #ABB2BF default syntax (foreground)
 * #828997 medium syntax
 * #5C6370 darkest syntax
 * #56B6C2 cyan
 * #61AFEF blue
 * #C678DD purple
 * #98C379 green
 * #E06C75 light red
 * #BE5046 red
 * #E5C07B light orange
 * #D19A66 orange
 * #282C34 background
 * #528BFF accent
 * @syntax-gutter: darken(@syntax-fg, 26%);
 * @syntax-guide:  fade(@syntax-fg, 15%);
 */

.ace-cloud9-night,
.ace-cloud9-night .ace_gutter {
  background: #282C34 !important;
  color: #ABB2BF !important;
  padding-right: 10px;
}

.ace-cloud9-night .ace_print-margin {
  width: 1px;
  background: #555651;
}

.ace-cloud9-night {
  background-color: #282C34;
  color: #ABB2BF;
}

.ace-cloud9-night .ace_cursor {
  color: #528BFF;
}

.ace-cloud9-night .ace_marker-layer .ace_selection {
  background: #3D4350;
}

.ace-cloud9-night .ace_multiselect .ace_selection.ace_start {
  box-shadow: 0 0 3px 0px #282C34;
}

.ace-cloud9-night .ace_marker-layer .ace_step {
  background: rgb(102, 82, 0);
}

.ace-cloud9-night .ace_marker-layer .ace_bracket {
  margin: -1px 0 0 -1px;
  border: 1px solid #ABB2BF;
}

.ace-cloud9-night .ace_marker-layer .ace_active-line {
  background: #202020;
}

.ace-cloud9-night .ace_gutter-active-line {
  background-color: #272727 !important;
}

.ace-cloud9-night .ace_marker-layer .ace_selected-word {
  border: 1px solid #49483E;
}

.ace-cloud9-night .ace_invisible {
  color: #3B4048;
}

.ace-cloud9-night .ace_entity.ace_name.ace_tag,
.ace-cloud9-night .ace_meta.ace_tag,
.ace-cloud9-night .ace_constant,
.ace-cloud9-night .ace_storage {
  color: #E06C75;
}

.ace-cloud9-night .ace_keyword{
  color: #61AFEF;
}

.ace-cloud9-night .ace_punctuation,
.ace-cloud9-night .ace_punctuation.ace_tag {
  color: #ABB2BF;
}

.ace-cloud9-night .ace_constant.ace_support.ace_fonts,
.ace-cloud9-night .ace_constant.ace_character,
.ace-cloud9-night .ace_constant.ace_support,
.ace-cloud9-night .ace_constant.ace_language,
.ace-cloud9-night .ace_constant.ace_numeric,
.ace-cloud9-night .ace_constant.ace_other {
  color: #D19A66;
}

.ace-cloud9-night .ace_invalid {
  color: #F8F8F0;
  background-color: #F92672;
}

.ace-cloud9-night .ace_invalid.ace_deprecated {
  color: #F8F8F0;
  background-color: #AE81FF;
}

.ace-cloud9-night .ace_support.ace_type {
    color: #ABB2BF;
}

.ace-cloud9-night .ace_constant.ace_language.ace_escape,
.ace-cloud9-night .ace_keyword.ace_operator,
.ace-cloud9-night .ace_support.ace_function {
  color: #56B6C2;
}

.ace-cloud9-night .ace_fold {
  background-color: #A6E22E;
  border-color: #ABB2BF;
}

.ace-cloud9-night .ace_storage.ace_type {
    color: #C678DD;
}

.ace-cloud9-night .ace_support.ace_class {
  font-style: italic;
  color: #66D9EF;
}

.ace-cloud9-night .ace_entity.ace_other,
.ace-cloud9-night .ace_entity.ace_other.ace_attribute-name,
.ace-cloud9-night .ace_variable {
  color: #D19A66;
}

.ace-cloud9-night .ace_string,
.ace-cloud9-night .ace_list.ace_markup,
.ace-cloud9-night .ace_constant.ace_language.ace_escape .ace_string,
.ace-cloud9-night .ace_string.ace_attribute-value {
    color: #98C379;
}

.ace-cloud9-night .ace_entity.ace_name.ace_function {
  color: #61AFEF;
}

.ace-cloud9-night .ace_operator {
    color: #ABB2BF;
}

/*.ace-cloud9-night .ace_string, */
.ace-cloud9-night .ace_identifier,
.ace-cloud9-night .ace_variable.ace_parameter{
  color: #ABB2BF;
}

.ace-cloud9-night .ace_comment {
  color: #5C6370;
  font-style: italic;
}

/* VIM mode cursor */
.normal-mode .ace_cursor {
  border: 1px solid #528BFF;
  background-color: #528BFF;
}

/* c9 tabs */
/*.tab_shadow {*/
/*  display: none !important;*/
/*}*/
.editor_tab .btnsesssioncontainer {
  background: #282C34;
}
.tab_middle:before,
.tab_middle:after {
  display: none !important;
}
.session_btn {
  border-radius: 2px 2px 0 0;
  margin-top: 1px;
  margin-left: -1px;
  min-width: 120px;
  padding-right: 10px;
}
.session_btn.curbtn{
  margin-top: -2px;
  min-width: 120px;
}
.session_btn.curbtn .tab_middle {
  margin-top: 0px !important;
}
.session_btn.btnclose .tab_middle .sessiontab_title {
  margin-left: 0;
  margin-right: 0;
  padding-left: 8px;
  text-overflow: ellipsis;
  margin-right: 10px;
}
.session_btn strong,
.has_apf .session_btn strong:hover,
.has_apf .session_btn strong:active,
.has_apf .session_btn.curbtn strong:hover,
.has_apf .session_btn.curbtn strong:active {
  margin-right: 12px;
  z-index: 1000000;
}
.session_btn {
  padding: 0;
  margin-right: 0;
}
.editor_tab .btnsesssioncontainer {
  padding-left: 25px;
}
.session_btn .tab_middle {
  background-image: none;
  margin: 0;
}
.editor_tab .btnsesssioncontainer {
  background: inherit;
  box-shadow: none;
}
.c9-simple-btn.plus_tab_button {
  margin: 2px 0 0 5px;
  transform: none;
}
.c9-simple-btn.plus_tab_button:after {
  font-weight: bold;
  text-align: center;
  content: '+';
  border-radius: 50%;
  background-image: none;
  color: #333;
  background-color: #bbb;
  transform: none;
}
.c9-simple-btn.plus_tab_button:hover:after {
  background-color: #fff;
}

/* pug classes */
.ace_class.ace_jade {
  color: #C678DD;
}

The original syntax theme is from https://github.com/pslobo/Quiver-Theme-Atom-One-Dark
which is a port of Atom's One Dark theme.